No one else has answered your actual question yet, so let me:
Running installed pirated Wii U games actually does not require the console to be hacked. You need homebrew in order to install them (which is placed on the SD card and requires an exploit ran through the web browser, or a hacked DS game which is also installed through said web browser exploit) but once installed, they can be ran without any hacks at all. At least, that's the case for retail games. eShop games and DLC require CFW both to be installed and ran. For example, Zelda BotW could be played without any hacks at all once installed, but if you wanted the DLC without paying for it, you'd need to use CFW when installing, and launch CFW before playing it every time.
My guess is that the previous owner used the web exploit, or had Haxchi installed, installed all of those games, and before selling the console, simply removed Haxchi (if installed) or otherwise left the console the way it was, since without launching an exploit, the console is completely unmodified. In order to launch the homebrew on the SD card you'd need to use said web exploit.